LEDs have been widely used due to their remarkable advantages like high brightness, small size and high efficiency. Based on red or green LEDs, LEDs with high brightness are developed which emit light in blue/UV wave band. One example is white LEDs that produce visible white light combined with blue/UV light via fluorescent material. Consequently, the encapsulation material for LEDs needs to resist blue or UV light.
Epoxy resin-based compositions cured with acid anhydride are conventionally used as encapsulants for LEDs. U.S. Pat. No. 7,125,917 B2 discloses an epoxy composition with antioxidant and phosphor-containing compound that is used as LED encapsulant. Generally, despite excellent transparency of epoxy resins, they show disadvantageous photo-degradation under blue/UV light and resultant discoloration. Furthermore, the heat produced in high brightness LEDs will even deteriorate the discoloration and as a result it will hamper the light transmittance and consequently shorten the life span of LEDs.
As another encapsulant, silicone resin has been mainly used in high brightness LEDs due to its high light & heat-resistance. However, problems occurred insofar as silicone encapsulants are prone to deform and consequently increase the possibility of breakage of LEDs bonding wire. Therefore, improvement of mechanical properties is necessary. Furthermore, the low adhesiveness of silicone encapsulants might result in peeling between device and the seal during heat shock.
Hence, it is necessary to find a solution to balance the optical and mechanical properties of the encapsulant. Patent application US 20050123776 A1 discloses an epoxy-silicone hybrid composition and its cured product having improved properties of adhesiveness, heat and moisture resistance. However, disadvantages of low discoloration resistance in white LEDs can not be excluded.
Patent application CN 101148542 A discloses a hybrid acrylate-silicone composition to reach improved transparency and higher discoloration resistance under heat and blue/UV light.
Generally, there exists an ongoing demand for improvement of crosslinking behaviour and subsequently the integrated mechanical properties of silicone compositions for practical application in LEDs.
Thus, the object of the present invention is to provide a resin composition which exhibits excellent transparency and mechanical strength as well as high resistance against heat and photo-degradation.